What is a primary factor in determining aircraft movement on the ground?

Control Tower instructions are the primary factor in determining aircraft movement on the ground because they provide essential guidance and coordination for all aviation activities at an airport. The control tower is responsible for managing air traffic on the runway and taxiways, ensuring that aircraft movements are safe and efficient. This includes directing taxi routes, takeoff and landing sequences, and maintaining safe distances between aircraft.

While factors like weather conditions can influence operations and personnel availability can affect schedules, it is ultimately the control tower's instructions that dictate the immediate movement of aircraft in and around the airport. These instructions are critical for managing traffic flow and minimizing the risk of accidents on the ground, thereby making them a crucial component of aircraft movement operations.